The Toronto-based company, however, said it remains confident in the long-term viability of the mine, expected to produce 60,000 to 75,000 ounces in the year ending December, nearly half its previous forecast of 110,000 to 130,000 ounces.

"We and the other companies mining underground in the region know that this district is prone to seismic activity and we are taking the necessary measures to keep our excellent safety record intact," president and CEO Steve Letwin said in a statement.

"Westwood is still in its infancy and similar to mines in the area, we expect it to have growing pains as we gain operational experience in this mining environment."

On May 26 Iamgold had to halt production at Westwood, one of its smallest and newest mines that is still in ramp-up mode, after a rockfall.

An initial assessment was inconclusive in evaluating the impact on production, but further investigation showed the event would "have a more significant impact on 2015 production than originally indicated", the miner noted.

As a result, Iamgold is forecasting now it will produce 780,000 to 815,000 ounces for the year ending December, down from 820,000 to 860,000 ounces previously estimated.

The company stock was down 3.2% at Cdn$2.60 at 10:14 am ET on the Toronto Stock Exchange. Through Friday, it had fallen nearly 38% in the last 12 months.